(1) Field of the Invention
The invention is concerned with methods for the preparation of structured particle latexes. The polymer particles comprising the latex have stabilizing, pH independent ions which are chemically bound at or near the surface of the particles.
(2) Description of the Prior Art
Latexes require some means for providing colloidal stabilization in aqueous media. The usual colloidal stabilization is provided by surfactants which usually are anionic or cationic but may be nonionic, especially in mixtures with anionic or cationic surfactants. Even though they contribute to the required colloidal stability, the surfactants can interfere with coating performance of the latexes even though the amount is limited and less than the desired stability is obtained. Another method is to copolymerize with nonionic monomers a small proportion of an ionic monomer to prepare a stable latex with little or no conventional surfactant as described in U.S. Pat. No. 3,637,432. Such processes, however, require special combinations of monomers and special polymerization techniques. Although such processes produce latexes having little or no surfactants, varying amounts of water-soluble products are made during carrying out of the process and remain in the product.
Aqueous colloidal dispersions (latexes), stabilized by adsorbed interfacially spreading polyelectrolytes, are described in U.S. Pat. No. 3,965,032. Latexes made by that approach have excellent stability and are particularly useful in application like coatings where conventional surfactants interfere with performance. However, in some cases (e.g., beater addition), the adsorbed polymer layer can be desorbed causing interference with deposition and thereby limiting utility.
Methods of forming structured particle latexes by polymerizing a layer of reactive nonionic copolymer onto the particle surface and then converting, by a subsequent reaction, that layer into a cationic polymer bound to the particle surface are described in U.S. Pat. Nos. 4,056,501 and 4,002,586. In each of these patents, the process requires at least three steps: preparation of the initial latex, capping and post-reaction to form the desired product. Moreover, the products should be freed of the reactive monomers and residual post-reactants before use. In many instances, this step is difficult. For many applications, it would be desirable to have a more economical process.